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This is Hacker Public Radio episode 3772 for Tuesday the 17th of January 2023.

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Today's show is entitled, Adventures with a small solar panel.

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It is hosted by Andrew Conway and is about 28 minutes long.

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It carries a clean flag.

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The summary is I have a look at a cheap solar panel and learn a bit about how it works

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and doesn't work.

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Hello and welcome to another episode of Hacker Public Radio with me, McNally, also known

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as Andrew.

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And in this episode I'm going to tell you a little bit about my adventures with solar panels.

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Not all about them because I can probably go on for a long time.

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It's actually literally about how I've discovered that solar panels work.

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And most of this you can read by Googling around web searching, should I say around in the internet.

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But I found that two things, which is quite usual when I'm trying to learn something.

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The first is there's a lot of rubbish in the internet, a lot of stuff that's plain wrong

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in misleading.

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Probably more than there used to be.

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But secondly, something you just learned best by doing.

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So this is all pretty much the first hand knowledge from me.

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Okay.

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So my first balance with solar panels was a small little low voltage, almost a toy type solar

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panel.

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It was, I guess, this is about the size of an A4 sheet of paper, you know, a side of a normal

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notebook.

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And it could claim, it could generate, I think, six to seven watts.

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And maybe it could, if I took it inside the Earth's orbit, perhaps, the distance of

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Mercury, Venus from the Sun, maybe then it could.

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But here in the Earth, I couldn't get much more than five watts out of it.

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And that was in a very good day with the panel pointed straight to direct sunlight.

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So my first thing was, it don't believe what's written on the label.

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Now actually, subsequently, with more professional panels that are designed for generating

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serious amounts of electricity for putting in your roof, for example, the specifications

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are done according to much tighter standards.

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But these smaller solar panels, not so much.

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So don't necessarily believe the, you're going to get the power that you think you will

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out of them.

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The other thing I discovered about solar panels very quickly was that they don't behave

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at all like any power source that I've dealt with before.

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Now the most common type of power source that I deal with, and I imagine most people deal

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with, is means voltage electricity.

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And you have a socket, three pin here in the UK, maybe other countries have more usually

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two pins, I don't know.

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But generally, the point of this is that you plug your device into the wall, an outcome

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of electricity, and if you plug in a electric toothbrush, or if you plug in a 30 kilowatt

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oven, or some kind of space heater, there's many kilowatts, you'll get the power,

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lamps will be delivered, and the voltage will hold up.

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So in this country, I expect where I am at 230 to 240 volt pretty constantly, and when I plug

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something in the voltage that doesn't drop appreciably, in fact, if it did drop by many

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volts, it would be time to investigate what the problem was.

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So in other words, what I'm trying to say is you get the power within reason, the current

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draw the power from your constant voltage source, and your voltage doesn't drop when

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you put a load on it, or the drop is negligible.

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So moving on to the next, most common source of electricity, which is batteries, now batteries

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are a little bit more delicate to deal with, because when you draw anything but the small

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current from a battery, you will notice quite a sizeable drop in the voltage, and of

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course, other different sort of batteries, of course, is that they are DC, direct current,

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so there's no in main voltages oscillating here, in the UK, it's 50 times per second,

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50 Hertz, but a battery just delivers a straight constant voltage, or a straight constant current,

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with no variation unless the load is asking for a varying amount of current.

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So the key thing here is that when you draw even fairly modest amounts of current from a small

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battery is voltage will drop, now the device, most devices are designed to expect that,

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in fact, they're designed to handle the fact that the battery's voltage will drop, so when you

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buy a AA battery, or a AAA battery, it's rated at 1.5 volts when you get it, but it

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time it goes flat in inverted commons, and I'll tell you why I say inverted commons, it may

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be done to say 1.2 volts, and the devices are designed to work down there, and then make

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give you a warning, or in the case of a small torch, or flashlight, the device may just

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quit working completely, and with no warning. Now the reason I said flat in inverted commons

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is because just because it's a 1.2 volts doesn't mean it's got no energy left, in fact,

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it could have depending on the type of battery as much as 50% of its energy left,

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but it just can deliver a voltage that's useful for the purpose that you bought it for,

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so you discard it and you don't think much of the fact that you've just thrown away some

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potentially useful energy. There is a way to get energy out of such low voltage batteries, it's

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called a dual-feet, and maybe I'll do another HPR episode about that at some future point. Anyway,

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I digress, the point is that a battery will not give you a constant voltage, they won't give you

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the voltage, it's written on it, you're running it down over time, or because you placed a high

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current load in the battery. So that means that you have to design your circuits with that in mind.

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Now, the big surprise with solar panels, I didn't really know much about them, is that there

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are an extreme version of what happens with batteries, so I could hook up this little plastic solar

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panel that I bought. The brand name was Sunny Solar, good luck if you try and look that one up.

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It's almost certainly some meaningless brand name that's been pasted on from some generic product

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that's been turned out in a Chinese factory somewhere. I'm sure there's many other identical

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products with different names, but this particular solar panel, as I see, was rated at, I think it's

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a claimed it could do six volts at a deliver one amp, I think that's was the origin of why it

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claimed it could do six watts. Now, when I plugged it in and and fill sunlight, I could for a

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time get about six volts, or even a shade more. I noticed that the two things, first full of

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voltage would drop, not rapidly, but slowly and then come to a stable value, 5.9 or 5.8 something.

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Now, I'll be the first thing I noticed. The second thing, and this is the really dramatic

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thing, is that, oh, I've got, oh, I've got just about six, six volts, the play with here.

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Okay, that's plenty for my application. Maybe a bit too high for some of my devices, but here we go.

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But the interesting, you plug in a device to it, nothing happens, or maybe you see a pretty

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flash of an LED or something, and then it just dies, I think, oh, what's going on here.

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And when I connected an ammeter, the first thing that I noticed was, well, if actually

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in direct sunlight, it blew up the fuse in my ammeter, because I had it in the low current range,

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so, so, another lesson for you is, always go for the, if you've got one of these multimeter,

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I'm saying that ammeter, but it's a multimeter, especially the cheap ones, make sure, make sure,

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you put it on the 10 amp range, not the low range for looking at milliamps and microamps,

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because if you don't, then you'll blow a fuse which has maybe only rated to a few hundred milliamps.

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That was the first thing I learned. But when I realized what was wrong with my multimeter,

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and connected up in the 10 amp range, so I was nice and safe, I saw that maybe very briefly I would

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get the high current, like, I don't know, many hundreds of milliamps, maybe if it was full sunlight,

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but it would quickly vanish, and the voltage would collapse, and I would be left with nothing.

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I thought, okay, what's going on here then, and you have to really understand how a solar

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panel works. So, there are two key panel parameters on the specifications to the solar panel.

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Well, there's three. The one that most people describe as solar panel with is the power rating.

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So, in this case, it was, it claimed to be sex watts, I think. We'd be actually even seven,

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depending on the sales brochure you happen to look at. Anyway, let's say it's sex watts.

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But that actually isn't very interesting. More interesting is the numbers that lie behind it.

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So, it's said, voltage six volts and current one amp. Okay, now, I think what that really

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meant is that the open circuit voltage of the panel in full sunlight, so that's a sunny day

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of the panel, sun fairly high in the sky in the, and the panel pointed directly at the sun.

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So, it's absorbing as much sunlight as you can get on the panel.

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What it was saying is, at that point, the open circuit voltage of the panel should be sex

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volts, indeed it was. I measured sex volts. And the reason the voltage, I noticed dropped slightly

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as because as a solar panel heats up, it becomes less efficient. And, in fact,

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a cold solar panel is more efficient at producing electricity. Not hugely more efficient,

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maybe a one or two percentage points more efficient, depending how exactly how cool to get.

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So, I was observing is as the panel, which is dark in color and place it in the sun,

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it'll heat up quite rapidly to temperatures above 50 degrees C, maybe it's all predicting temperature

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could be as high as 70 degrees C, in fact. And so, there's quite a sizable

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change in efficiency because of this. And that's why I saw this voltage drop. Anyway, it's still

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roughly, give a take a few hundred millivolts, it's still your total torquey about six volts,

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in about plus and minus hundred millivolts, six, six volts. But that's the open circuit

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voltage. And that means that I have not completed a circuit that was effective

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to let infinite resistance between the positive and negative leads of the solar panel.

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That's what that parameter means, the open circuit voltage. So, you'll quite often see in solar

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panel specs, the subscript or C voltage in the open circuit. And that isn't the voltage you're

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getting because the moment that you connect a circuit to it, the voltage will drop.

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How far it drops depends on how much current you try to draw. So, if I tried to draw the one

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amp, it said in the label, it could do one amp. If I tried to draw one amp, I would not

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still have six volts. In fact, I have something very close to zero volts and I wouldn't have one

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amp either because the voltage wasn't there. And at this point, it's probably a good idea to fall

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back on the analogy of voltage and current being the pressure and flow of water. So, let's

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forget electricity for a moment. You have a hose pipe and you connect one into a tap or faucet,

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I guess, for my colleagues on the side of the Atlantic. And, of course, you open and close the

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nozzle at this point, if you haven't opened the tap and nothing happened. So, that's like

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the analogy there. The solar panel is in the dark and nothing is happening. There's no voltage,

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no pressure, no current is nothing. Then, you open up the tap. So, this is a bit like taking a

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solar panel out and placing it in strong sunlight. When you open up the tap, water pours in to the

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pipe and it's up hissing sound for a brief time and then it stops. And then all you're left with

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is a pipe full of water that's at pressure. And it's the means, in the case of the water pipe,

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it's whatever your means pressure of your water system is connected to the tap. But that's the key thing,

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you've got a nice high pressure. Now, when you open this, so I should say this at this point,

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this is a bit like taking a solar panel and leaving it in sunlight. And you'll see this high

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voltage, in the case of my solar panel, a six volt across the plus and minus leads. There's lots of

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voltage there. Just as there's a lot of separation in the pipe, but nothing else is happening. Water is

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not flowing out, electricity is not flowing out. So, all crazy static. That's useless. The moment you

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try to do something with the water, what happens is some of the pressure that was built up in the

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pipe is dissipated as the water flows out in a jet out of the nozzle. And that pressure is turning

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itself into the flow of water. So the pressure inside the pipe will drop slightly, but not

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to nothing, otherwise the water wouldn't flow the pipe. And the amount of water that's flowing

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out the pipe per second, let's say we measure it in liters per second. That is analogous to the current flow in the

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solar panel. Now, at this point, the analogy isn't so good because the main water is a bit like

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means electricity. It will supply within reason. You know, whatever pressure you need for the nozzle

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of your pipe. Now, if you close the nozzle at the end of your hose and then you went and close the

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tap, then there'll be water inside the hose and it will be held at quite high pressure because it

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can't go out through the closed tap or the closed nozzle. So this is like analogy of a solar panel

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in low sunlight. There's some charge stored there. There's next to nothing coming in. Or maybe you

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open the taps, like very slightly electrical water in, but they're just really not enough pressure

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to sustain it. So the moment that you open up the nozzle or at the end of the hose, water won't

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splort out and it kind of, yeah, come on the splort and then it will die down to trickle almost immediately.

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Because it's just no pressure at the end. Even if you have the tap open slightly to let some

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water in, there's very little pressure from that. So it will take too long for the hose pipe to fill

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up again. But if you did close the nozzle, the hose pipe would fill up again and you'd end up with

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a pressure ice pipe again. That's a bit like the idea of taking a solar panel, putting it in

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not very sunny conditions, but sunlight. Holding it to open the circuit voltage and then suddenly

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connecting something, the voltage will collapse. You'll get a sudden burst of current which may

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require accumulator as I discovered, but it can't sustain that current for any length of time

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and you'll just end up with a low voltage and an extremely low trickle of electricity, a low current.

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So that's how you should think of a solar panel. Now the more

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sunlight that you have, the greater the voltage it can sustain and the greater the current that

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you can draw off it without that voltage, completely collapsing, anything. So the game really is,

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is how much current can you pull out of a solar panel in the amount of sunlight that you've got?

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And that is a quite tricky problem really. But the answer is that you can sort of, you can

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tell from the voltage, roughly what level of sunlight that you've got. It will vary slightly

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in sunlight, but actually it's much better to look at the, what's the other parameter that we

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printed in a solar panel, and that will be, not the open circuit, but the short circuit current.

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So if you connect the plus and the minus leads to the panel, which you ordinarily never do

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with mean electricity or even a battery, because a solar panel is a small solar panel,

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low wattage solar panel, isn't going to damage anything and block the wires, you can do this

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quite safely. You can connect plus and minus leads together, and if you do so through an ammeter,

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a multimeter, I said to measure current, then you can measure what current is present when the

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resistance is negligible that we've got a short circuit. What you will find then is the amount of

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current, and that situation will be proportional to the amount of solar power falling on the solar

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panel. So if the sunlight goes from say, I don't know what to say, 100 watts per square meter,

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which is quite dim, really, there's a very coldy stormy day to 200 watts per square meter. So

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after a thunderstorm and things are brightening up again, you might see that, you will see maybe

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the current jump from pulling numbers out of thin air here, but let 100 milliamps to 200 milliamps,

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not my rubbish that'll solar panel, but a bigger one. So you'll see there's a proportionality between

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the short circuit current and the amount of power from sunlight falling on your solar panel.

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And that's, so that is a way that you can start to understand how the solar panels parameters

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do relate to the sunlight. You can do it with voltage, but I think it's quite a week and non-linear

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relationships. But it still hasn't really answered the question that I was getting to

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how much power can you draw from that solar panel and given light conditions? Well, it doesn't

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answer, I haven't got to that answering that question, but before I do, it makes sense of the

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stats that are printed in my solar panel. It's said six volts, that was the open circuit voltage. So

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that's where I'm not drawing any load whatsoever from the panel, useless. I can in theory draw

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one amp from the panel by providing zero resistance by connecting the plus and minus leads together.

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Again, yes, I get the current, but there's no power associated with that, because it's nearly at

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zero volts when I do that. So in both cases, there's a negligible amount of power.

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Somewhere between those two extremes is where we want to be. So we want to find a value of

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current draw from the solar panel. We're equivalently a voltage that we want to keep the solar

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panel at that maximizes the amount of power. Now, it turns out that for any given level of sunlight,

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there is such a point, it's called the maximum power point, and I can't really describe a graph,

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I'm not going to try and describe a graph, but if you look at maximum, such up in maximum

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power points, solar panels, you'll see these graphs of current versus voltage, where the current

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is plotted in the vertical axis and voltage on the horizontal axis, and there's a constant current

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up to some voltage, and then the voltage just disappears. When you try to draw current, and

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sorry, sorry, the other way around, the current disappears when you try to hold that panel

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at a high voltage. And yeah, I said I wouldn't try and describe the graphs, and I have gone and tried

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to describe the graphs, and now if I confuse myself and probably use so I apologize for that. Anyway,

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forget that I confusing the description of the graph. The point is, there's a current

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and a voltage for any given set of the sunlight where you want to be at to maximize the power

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draw. And if you're at full sunlight, then in theory you should get the wattage

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rating of the solar panel. That's a full sunlight with the panel perpendicular to the sun's

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rays. Now, for a big professional panel, which I do have some of,

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that those specifications are trustworthy and an information is regulated. The solar panel

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companies are played by the rules by and large. For a cheaper one, you get from hobbyists,

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stores online, the lower wattage ones a few, a few watts up to maybe it doesn't,

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a couple doesn't watts. Yeah, watch out, you probably will get misleading specifications.

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So what this panel should have said to me is that six volts was the open circuit of voltage,

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and one amp was the short circuit current, and it should never have quoted a power rating of

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six watts or whatever. That's just raw. And a good day, I can maybe cook for what, maybe a little

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bit more than four, maybe four and a half watts out of it, if I'm really on the ball.

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And what does really on the ball mean? Well, it's finding one way you can do it is just connect

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different values of resistors between the plus and minus leads until you find the one that

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gives you the maximum power rating. You have to be a bit careful because most common resistors

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are rated at a quarter of a watt, and you will literally see even with a small solar panel,

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it does five watt. You will literally see the resistor disappearing the puff of smoke, if you managed

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to try and pass several watts through it, you can buy bigger resistors. But actually,

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much better idea is to rapidly, using pulse width modulation, open and close the circuit

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to try and regulate the voltage in the current draw. And those devices are called pulse width

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modulation, so a charge controllers. And if you want to get a bit more juice and make sure you're

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finding that maximum power point, then you can use these so-called MPPT solar charge controllers.

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They also use pulse width modulation, but then rather and more intelligently will hunt down

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that maximum power point that I was talking about. And they will adapt to, as a level of

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sunlight changes, they'll adjust the current draw to keep the maximum power flowing out. Now,

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of course this has a problem. If you've got electronics, let's say, for example, like an ESP32 micro

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controller, it really only wants 3.3 volts, and it's tolerance, it's not going to like it if you

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give it five volts because the sun's come out. So the solar charge controllers, other job,

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is not just to find the maximum power point, but it's to output a reliable level of voltage.

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Generally, they will output 5 volts for these hobbyist ones. For larger ones, for charging battery

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storage and households, you'll typically see the output voltage of the solar charge controllers

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at something that will charge either a 12 volt, a 24 volt, or even a 48 volt battery. So my

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house, this is for a future HPR episode, I've got a 24 volt system, that put together myself, but that

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uses a rather chunkier and more expensive charge controller. But for the one for the small solar

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panel, I got this, I think I bought it from Pymaroney or Pi Hut, I can't remember which we

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are bought exactly, but it was called, the brand name was DF Robot, and it was just ideal for

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taking the power delivery by the small solar panel and outputting it at 5 volts, literally through

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USB, and it also allowed me to charge a connected battery if I really had to connect a battery

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for it to work properly. And you could plug in USB from another source and charge the battery

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with all solar power so you can do both. So it's quite a clever little device. The thing is that if

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you only had solar power, you couldn't, and the sun went behind the cloud, then the five volts

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output will collapse. So you really need a battery and the solar panel together, in order to smooth

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out the tremendous variation in power delivery, the solar panel is going to give you, you know,

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because of a cloud going from the sun or suddenly walking in front of the sun, or the sun moving

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behind the tree, or all these kind of things. So the other lesson I learned was really solar panels

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by themselves are not that great. You need to have another power source to work with them. Either

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they offset what you're drawing from the grid in some way, or unless it's been my preference,

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is that you have a battery in the battery stores the power when the sun is shining,

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you're charging up the battery and powering the load. And when the sun isn't shining, then the battery

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takes over and can deliver charge. And so in this way, you can run pretty much indefinitely low

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power electronics. With a small solar panel, you could probably, and not probably, you can definitely

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run an ESP32 night and day pretty much indefinitely, even through a Scottish winter. I've discovered

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it's quite possible. If your battery can take in enough charge when it is sunny, probably a small

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five watts solar panel is going to do the job and keep your device topped up and powered through

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long nights here in Scotland. So yeah, that's really all I've got to say about solar panels.

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I might do future episodes. If people are interested, and I'm interested, which I probably

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will be to be honest, on my larger solar panels, I've got two sets on the go one from my house,

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and one observatory that I've been involved in building with Astronomical Society of Glasgow.

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And so that's a different game. You're dealing with mains voltage coming out of inverter,

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you're dealing with solar panels that can output kilowatt and that will arc and spark.

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And DC circuit breakers that can burst into flames in all kinds of exciting things.

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And you can electrocute yourself and blow up multimeter and oh yes, it's a whole level of new

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fun to be hand with those. So I'll just end that with the warning as it's very safe to play around

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the these little voltage solar panels. So if you want to play play with them,

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be very careful playing with the big boys and girls. The high, when you're dealing with hundreds

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of watts, kilowatt solar panels are a and inverters, which help it means electricity. You have to be

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much more careful and also you're dealing with DC. So that's again, as I say, different from

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dealing with AC. So if you do go up, if you do want to play with bigger solar panels,

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I do advise some caution as they can be surprisingly fun. Should we say any, I'll leave it there.

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If I've got anything wrong or could it explain better, please do leave comments and or do a show

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of your own. If you've got solar panels, I'd love to hear your experiences. I've got certainly plenty

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more to learn myself. So I'd love to hear other views on how people have got on with their solar panels

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out there in the Hacker Public Radio Land. Okay, thanks very much, listening. Bye bye.

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